The Impact of Multiple Species Invasion on Soil and Plant Communities Increases With Invasive Species Co-occurrence

Abstract

Despite increasing evidence indicating that invasive species are harming biodiversity, ecological systems and processes, impacts of multiple species invasion and their links with changes in plant and soil communities are inadequately documented and remain poorly understood. Addressing multiple invaders would help to ward against community-wide, synergistic effects, aiding in designing more effective control strategies. In this work, correlative relationships are examined for potential impacts of three co-occurring invasive plant species, Amorpha fruticosa, Fraxinus pennsylvanica, and Acer negundo, on soil conditions and native plant diversity. The research was conducted in riparian ecosystems and included the following treatments: (1) co-occurrence of the three invasive plant species, (2) occurrence of a single invasive species, and (3) control, i.e., absence of invasive species. Co-occurrence of three invasive plant species caused higher direct impact on soil properties, soil functioning, and native plant diversity. Soil in mixed plots (those populated with all three invaders) contained higher levels of nitrifying bacteria, organic matter, nitrogen, and carbon as well as lower carbon to nitrogen ratio as compared to single species invaded plots and control plots. Furthermore, native plant diversity decreased with invasive plants co-occurrence. Differences in soil conditions and lower native plant diversity revealed the interactive potential of multiple invasive species in depleting biodiversity and eroding soil functionality, ultimately affecting ecological and biogeochemical processes both below and above ground. Our results highlight the need to prevent the impact of multispecies invasion, suggesting that riparian ecosystems affected by co-occurring invaders should be prioritized for invasion monitoring and ecological restoration.

A nature-positive future with biological invasions: theory, decision support and research needs

“…Research on the community-level consequences and management of multispecies plant invasion is growing (e.g. [ 26 , 36 , 44 ]), and more studies of mixed-species animal communities have been called for [ 41 ]. In practice, information on the structure and function of mixed species communities serves a different and complementary purpose to understanding the ecological processes outlined above.…”

“…For example, alien species in mixed-species animal communities can have superior performance for several traits compared to native community members (such as growth rates, physiological tolerance or higher fecundity), although such animal community-level studies are rare [ 41 ]. In general, introduced and native plants are phylogenetically similar and their traits are functionally distinct when contrasted with co-occurring natives [ 58 ], although at local, in situ community to landscape scales, these patterns can vary and be scale-dependent [ 44 ]. In plant communities, community-wide traits such as seed mass, specific leaf area and herbivore resistance have been shown to be correlated with invasion success at particular spatial scales and points of time in the invasion process [ 21 , 59 ].…”

Four Invasive Plant Species in Southwest Saudi Arabia Have Variable Effects on Soil Dynamics

“…Invasive plant species can outcompete and reduce the abundance of native plant species [ 42 ], alter soil properties [ 26 ], and homogenize the biodiversity of invaded communities and ecosystems [ 43 ]. Invasive plant species may alter soil properties in their new ranges, but the magnitude and direction of these changes are sometimes unique to each invasive species and often vary among habitats for the same non-native species [ 6 , 8 , 12 , 32 , 33 , 44 , 45 ]. To the best of our knowledge, this is the first study to investigate the biogeochemical consequences of the invasion of Prosopis juliflora , Ipomoea carnea , Leucaena leucocephala , and Opuntia ficus-indica in Saudi Arabia.…”

“…Other studies have reported no statistically significant difference among the properties and microelements of soils from habitats infested with invasive plant species compared to the soils of equivalent habitats occupied by native plant species [ 6 , 8 , 12 , 32 , 33 ]. Moreover, several studies that have compared the capacity of multiple invasive species to alter soil properties within the same experiments design have revealed contrasting results among the species examined [ 6 , 8 , 32 ]. Other studies have reported that the same invasive species alters soil dynamics in different ways in different habitats (communities) or under different experimental conditions [ 6 , 8 , 12 ].…”

“…However, recent assessments of invasive plant species highlight the need to distinguish between non-native (invasive) species that have minimal ecological consequences and non-native species that have major ecological consequences in their new habitats [ 30 , 31 ]. There is ample evidence that invasive species can alter ecological processes and reduce native biodiversity, yet the ecological consequences of invasive tree species and how they modify soil properties and conditions are still not well understood and not adequately documented [ 32 ].…”